A quick tip and reminder to prevent your cotton shirt from ever shrinking after a wash:

AVOID HEAT. It's the most important rule because cotton is a very sensitive material and reacts to heat badly.
You can pretty much do anything else you want to a T-Shirt and it won't shrink as long as it stays away from heat.

To wash your T-Shirt and guarantee it won't lose it's size, here are some tips:
1. Turn the t-shirt inside out and always put in a machine wash COLD CYCLE with a mild detergent specifically made for cold wash. Hand washing
in cold water is recommended too.
2.NEVER put your t-shirts in the dryer, but if you must, use tumble dry on low heat settings only for short durations.
Let your T-Shirts AIR-DRY by hanging them is the best option. Remember, no heat, so leaving your t-shirt in the sun is also
bad for it. Find a warm room with good airflow. The t-shirt should take 12-24 hours to dry.
3. To get the wrinkles out of the shirt, try a de-wrinkle spray or iron on very low heat (use parchment paper to protect printed images & vinyl).
4. No bleach or dry cleaning.